Recently, We got a new mobile to carry radios. It's a slightly used Honda Metropolitan II. These are nice little water cooled 4 stroke mopeds, smooth running, easy starting. It's got a nice big 22 liter luggage compartment under the seat to mount radios in (did I mention the 12 volt electrics?). Best of all, I figure I'm getting around 100 miles to the gallon.
By the way: You meet the nicest people on a Honda. In the first 4 days of ownership, about a dozen people have come up to me and complimented me on its styling, its quietness, how smart I am to wear a helmet, whatever. We chat about gas mileage (Hmm, under $2 for 100 miles... at $1.69 a gallon, that sure beats just about everything else! (I used to ride a Spree. That thing took about $.25 of gas a day... for 5-6 hours of riding. Or so it seemed.)) One fellow chatted about how he rented one on holiday down in Key West, and he put 80 miles on it in 2 days.. and how much fun he had riding, for the first time in years! And this is a fellow who rides Gold Wings!
The opportunity for success here: (can you tell I've been to "leadership training"? I don't get "problems" - I get "Solution Opportunities"!) Honda also makes a Metropolitan (no "II") which goes faster. The Metropolitan II seems to go about 25mph, whereas I'm told the Metropolitan will go around 40mph. After a little research on the web, Other people have also wanted their bikes to go faster.
Now a word on legality: check your state's laws regarding what a moped is. Don't change your moped into a motorcycle! If you do, you now need a motorcycle driver's license, more expensive license plates, more expensive insurance, and probably a new parking spot (in Wisconsin, a Moped can park where a bicycle can park. A Motorcycle, however, can only park where a car can park). In Wisconsin, which is what's important to me at the moment, a moped is defined as:
I got this information from a google search: "Wisconsin moped law". Hopefully, your state is progressive enough to put all the rules of the road and state statutes right on the web, too. If not, wander on down to your local library - Librarians are terribly resourceful people when it comes to looking things up. And, I just happened on a potentially helpful site: mistermoped.com/laws.html links to various DOT/DMV pages.
So: I've reviewed the law, and I'm confident that I can do 2 things:
What can be done? The Metropolitan II (vs. Metropolitan) has a whole lot of differences which keep it slow. The ones I'm aware of:
Intake Restrictor Plate: This insidious little beastie is a tiny (approx 2" x 1") piece of aluminum sheet metal which reduces how much air can get from the carburetor to the cylinder. As far as I can tell, this limits the engine's top speed - it can only suck in air fast enough for a certain RPM. (This limits top speed)
Carburetor Diaphragm Spring - This squirts gas into the engine (essentially). A shorter spring lets in more gas. More gas = more go. (This improves acceleration)
Variator - Part of the CVT. The difference here is that the Metropolitan II doesn't allow for as low of a gear ratio, again limiting the speed. No, I won't try to explain what a CVT is or what it does. Well, OK. A CVT is the common way to put an automatic transmission on a Moped. You've got 2 pulleys and a belt. Spin one pulley (with the engine), the belt moves, and spins the other pulley (which spins the rear wheel). The way you "change gears" is by increasing or decreasing the diameter of one of the pulleys (this is what the variator helps do). The pulley changes size (ahem) "Magically", depending on how fast you're spinning them. Anyway, the variator limits speed by limiting how much the pulley can change in size.
Final Drive Gear - Obviously if you can spin the back wheel faster, you go faster. Changing the Final Drive Gear for one with less teeth should make it spin faster... improving the top speed.
Engine Control Module - This changes when the lightning goes off (spark timing). Inside an engine, you've got this little lightning bolt factory. Whenever the lightning hits the gasoline, you get a little fire. The piston doesn't want its feet to catch on fire, so it runs away from the fire... while it runs away, it pushes the rear wheel around. When the fire goes out, the piston runs back to where it was sitting before, again spinning the rear wheel. Then there's another fire... and that piston keeps on running! (the Piston runs back and forth at least 30 times a second -- It'll drink some oil to keep cool) The ECM changes when the lightning bolts make the gasoline burn, increasing engine speed, and therefore making the bike go faster.
Camshaft - this changes how far the valves open. If the valves open farther, the engine can breathe better (good, remember?). If the engine can get the air it needs more quickly, it can spin faster...
FIRST: Make certain that everyone who drives the bike will still be able to handle the bike after you upgrade it. This sounds obvious, but it's a good point to remember. Suppose you and your kid sister share a moped. Sure, you can handle that extra speed and acceleration, but if you forget to tell little Jenny that you've souped up the scooter and she cranks on the gas and falls on her behind, she's going to be sad, and all big brother types know that kid sisters crying and telling Mom is generally a "bad thing". Understand that while I usually am the one driving the moped, my wife will occasionally take it out for a twirl. So I'm going to make sure that she knows how to handle it "stock" before I even think of upgrading it.
Second: Consider alternatives to souping up the bike's engine. You want faster, you could get a real motorcycle. You could add a windshield (lowers drag). You could leave earlier in the morning (this may require a new alarm clock). You ... get the idea. The point HERE, is don't break any laws. You did check your state's laws, right? Big Bore kits on Sprees are a stupid idea... they're no longer legal as mopeds, and they're still not fast enough to be useful as motorcycles. So unless you're trying to impress people with your alter ego of "Spree Racer", don't bother. Oh, and Spree Racer, most people will think you're insane, bordering on demented. Going 70mph on a Spree just isn't safe. I'm probably archaic, but I don't like the idea of breaking the law. I trust our legislators to only outlaw things that we really shouldn't do - like sell booze and cigarettes to kids, race on the highway, neglect to wear helmets and seat belts, or GO MORE THAN 30 MPH ON A MOPED.
This is a prime time for my soapbox. The brakes on a moped are really not designed to stop a vehicle traveling 70 mph. Mopeds typically lack footpegs - your feet WILL slide around in a collision. The operator position is not terribly well protected. The handlebars are not spaced for high-speed control. For me, the handlebars are too close to the operator position. Why? BECAUSE THE DESIGNERS AND MANUFACTURERS KNOW THAT YOU'RE NOT GOING TO GO VERY FAST SO YOU CAN'T HURT YOURSELF TOO MUCH. By souping up a moped, you're pushing it beyond it's design constraints. The adjustments I advocate do not push the vehicle beyond the bounds of legality or (IN MY OPINION) safety. YOU MUST MAKE SURE THAT YOUR VEHICLE IS SAFE AND LEGAL. Don't be an idiot and try to go 100mph on a moped - they're not built for it. Stick to 30mph, or whatever your state says is a good idea.
Third: Decide what you're going to do. Me, I plan on taking out the restrictor plate, and changing the carburetor spring (This should give the bike more zip and speed and still keep it legal). This should take around 1 hour, and I believe the easiest way to get to things will be through the luggage compartment. Of course, I haven't looked at the service manual yet.
To actually get to the engine (and carburetor and other goodies): Take out the 4 bolts under the seat. Note that there are 2 bolts which hold the seat hinge in: leave those alone. There are 2 up top by the seat latch, and 2 down inside the trunk which need to be removed. (10mm socket, extension, ratchet). Also, undo the phillips head screw which holds the kickstand lock handle in place. (#2 Phillips driver) Grasp the seat, lift.
You should now have access to the carburetor and restrictor plate. The restrictor plate is under the frame cross member (convenient!). Can be removed without dropping the engine. Take out the 2 bolts which hold the intake pipe to the intake manifold. (10mm combination or box wrench... although a 10mm GearWrench, if it would fit, would work splendidly for the left bolt... it's hard to get your fingers in there!) Wiggle the restrictor plate and green paper gasket loose, remove. (At this point, either discard, set aside, or modify the restrictor plate. Something like a Dremel tool could be used to grind out the restrictor plate to the same diameter as the intake pipe, so a superficial inspection would still "look" right, but your bike would go faster.) Reinsert the two bolts, and tighten down. (FYI: a previous owner ground out the restrictor plate on my bike. This greatly frustrated me once I got in there... a half hour or so, to accomplish nothing! I subsequently put the plate into storage.)
While you're in there, you may as well swap out the carb spring. There are 2 phillips screws that hold the top cover onto the carburetor body (one of them may have a wire retaining clip on it - fold that out of the way.) Remove both screws with a #1 Phillips screwdriver. Lift the top cover, and the spring should be right there to greet you. Swap (or modify) the spring, reinstall the top cover.
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